Under strongly basic conditions, tetrahalomethanes are known to generate chloronium or bromonium ions, which can be used to halogenate carbanions. The halogenation of ketones, sulfones, alcohols, and acidic hydrocarbons with perhalomethanes, e.g., CCl.sub.4, CBr.sub.4, CBrCl.sub.3, CCl.sub.2 Br.sub.2, in tert-butyl alcohol using powdered potassium hydroxide has been reviewed by C. Y. Meyers, et al., Catalysis in Organic Synthesis 1977, G. V. Smith, ed., pp. 197-278.
Halogenation reactions are also known to take place under conditions of phase transfer catalysis with a stoichiometric amount of aqueous sodium hydroxide as the base and benzyltriethylammonium chloride (TEBA) as catalyst (M. Majiszam et al., Rocz Chem. 1969, 43, 671-676; A. Jonczyk, et al., J. Org. Chem., 44, 1192-1194 (1979); S. E. Lauritzen, et al., Acta Chem. Scand. B 35, 1981, 263-268).
Active hydrogen compounds can also be chlorinated using 1,8-diazabicyclo[5.4.0]undecene-7 (i.e., "DBU") and CCl.sub.4 (Y. Hori, et al., Rikogakubu Shuho (Saga Daigaku), 1978, 6, 19-22); and brominated using DBU/BrCCl.sub.3 (Y. Hori, et al., Chem. Lett., 1978, 73-76).
U.S. Pat. No. 4,806,280, Mignani, et al., Rhone-Poulenc Sante (1989), discloses a process for preparing .alpha.-chlorinated unsaturated compounds with respect to two electron-attracting groups in the .beta.-position. The preferred halogenating agents are molecular chlorine, sulfuryl chloride, N-chlorosuccinimide, and hexachloroethane.